Plant oils are an important source of dietary fat for humans, representing about 25% of caloric intake in developed countries (Broun et al., 1999). World production of plant oils is at least about 110 million tons per year, of which 86% is used for human consumption. Almost all of these oils are obtained from oilseed crops such as soybean, canola, safflower, sunflower, cottonseed and groundnut, or plantation trees such as palm, olive and coconut (Gunstone, 2001; Oil World Annual, 2004). The growing scientific understanding and community recognition of the impact of the individual fatty acid components of food oils on various aspects of human health is motivating the development of modified vegetable oils that have improved nutritional value while retaining the required functionality for various food applications. These modifications require knowledge about the metabolic pathways for plant fatty acid synthesis and genes encoding the enzymes for these pathways (Liu et al., 2002a; Thelen and Ohlrogge, 2002).
Considerable attention is being given to the nutritional impact of various fats and oils, in particular the influence of the constituents of fats and oils on cardiovascular disease, cancer and various inflammatory conditions. High levels of cholesterol and saturated fatty acids in the diet are thought to increase the risk of heart disease and this has led to nutritional advice to reduce the consumption of cholesterol-rich saturated animal fats in favour of cholesterol-free unsaturated plant oils (Liu et al., 2002a).
While dietary intake of cholesterol present in animal fats can significantly increase the levels of total cholesterol in the blood, it has also been found that the fatty acids that comprise the fats and oils can themselves have significant effects on blood serum cholesterol levels. Of particular interest is the effect of dietary fatty acids on the undesirable low density lipoprotein (LDL) and desirable high density lipoprotein (HDL) forms of cholesterol in the blood. In general, saturated fatty acids, particularly myristic acid (14:0) and palmitic acid (16:0), the principal saturates present in plant oils, have the undesirable property of raising serum LDL-cholesterol levels and consequently increasing the risk of cardiovascular disease (Zock et al., 1994; Hu et al., 1997). However, it has become well established that stearic acid (18:0), the other main saturate present in plant oils, does not raise LDL-cholesterol, and may actually lower total cholesterol (Bonanome and Grundy, 1988; Dougherty et al., 1995). Stearic acid is therefore generally considered to be at least neutral with respect to risk of cardiovascular disease (Tholstrup, et al., 1994). On the other hand, unsaturated fatty acids, such as the monounsaturate oleic acid (18:1), have the beneficial property of lowering LDL-cholesterol (Mensink and Katan, 1989; Roche and Gibney, 2000), thus reducing the risk of cardiovascular disease.
Oil high in oleic acid also has many industrial uses such as, but not limited to, lubricants often in the form of fatty acid esters, biofuels, raw materials for fatty alcohols, plasticizers, waxes, metal stearates, emulsifiers, personal care products, soaps and detergents, surfactants, pharmaceuticals, metal working additives, raw material for fabric softeners, inks, transparent soaps, PVC stabilizer, alkyd resins, and intermediates for many other types of downstream oleochemical derivatives.
Oil processors and food manufacturers have traditionally relied on hydrogenation to reduce the level of unsaturated fatty acids in oils, thereby increasing their oxidative stability in frying applications and also providing solid fats for use in margarine and shortenings. Hydrogenation is a chemical process that reduces the degree of unsaturation of oils by converting carbon-carbon double bonds into carbon-carbon single bonds. Complete hydrogenation produces a fully saturated fat. However, the process of partial hydrogenation results in increased levels of both saturated fatty acids and monounsaturated fatty acids. Some of the monounsaturates formed during partial hydrogenation are in the trans isomer form (such as elaidic acid, a trans isomer of oleic acid) rather than the naturally occurring cis isomer (Sebedio et al., 1994; Fernandez San Juan, 1995). In contrast to cis-unsaturated fatty acids, trans-fatty acids are now known to be as potent as palmitic acid in raising serum LDL cholesterol levels (Mensink and Katan, 1990; Noakes and Clifton, 1998) and lowering serum HDL cholesterol (Zock and Katan, 1992), and thus contribute to increased risk of cardiovascular disease (Ascherio and Willett, 1997). As a result of increased awareness of the anti-nutritional effects of trans-fatty acids, there is now a growing trend away from the use of hydrogenated oils in the food industry, in favour of fats and oils that are both nutritionally beneficial and can provide the required functionality without hydrogenation, in particular those that are rich in either oleic acid where liquid oils are required or stearic acid where a solid or semi-solid fat is preferred.
There is a need for further lipids and oils with high oleic acid content and sources thereof.